1. Field of the Invention
The present invention relates to a laser power control device for controlling the output laser light radiating from multiple laser sources, and to an optical head employing this laser power control device for use in an optical recording and/or reproducing apparatus.
2. Description of the Related Art
Currently, optical recording and/or reproducing apparatus are generally equipped with a laser light source which is radiated onto an optical recording medium for information recording and/or reproduction. For these apparatus, it is necessary to pre-set the output power of the radiated laser light to a predetermined level. Laser power control devices are normally built into these apparatus to monitor and maintain the output power at the predetermined level.
Currently, a wide variety of optical recording mediums are commercially available. Many of these recording mediums use different recording densities. These different densities often necessitate the use of different wavelengths of laser light.
Optical recording and/or reproduction apparatus have been developed which can use several different laser wavelengths. This allows these apparatus to operate using several different optical recording mediums. These multiple medium apparatus currently employ independent laser power control devices to control the respective laser sources used by each medium. However, this use of separate laser power control devices makes it difficult to reduce the size of the apparatus. Moreover, the production cost of such multi-medium apparatus tends to be prohibitive.
Recent proposals have been made to fabricate multiple laser sources on a single monolithic chip and to arrange the sources close to one another. However, if the laser sources are arranged in close proximity to one another, it is difficult to provide independent laser power control devices for each laser source.
In view of the above problem, an object of the present invention is to control a plurality of laser sources using a single laser power control device.
Another object of the present invention is to provide a laser power control device capable of controlling the outputs of the respective laser light beams radiated from the plural laser sources.
A further object of the present invention is to provide an optical recording and/or reproducing apparatus using such a laser power control device.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and the drawings.
For accomplishing the above object, the present invention provides a laser power control device for controlling the output of respective laser light beams radiated from a plurality of laser sources, including a plurality of variable resistors associated with the laser sources, a sole photodetector associated with the laser light sources, and a laser output stabilizer for controlling the output of the laser light so that the output of the laser light radiated from the laser sources will be constant. The resistance values of the variable resistors are changed to set the output of the laser light radiated from the laser sources associated with the variable resistors. The intensity of the laser light radiated from the laser light sources is detected by the photodetector, and the output of the laser light is controlled by the laser output stabilizer, based on the detected intensity, so that the laser light beams output by the laser light sources will be constant.
The present invention also provides an optical head including a plurality of laser light sources, optical elements for radiating laser light beams radiated from the laser sources towards a recording medium, a light receiver for receiving the return light from the recording medium and a laser power controller for controlling the output of the laser light radiated from the laser sources. The laser power controller is of the aforementioned type.
With the laser power control device and the optical head, according to the present invention, the laser light power output from plural laser sources can be respectively controlled by a single circuit.